Electronic circuit breaker

ABSTRACT

The electronic circuit breaker comprises an input (A, B) for connection to a power-supply network and an output (C, D) for connection to a load (Z). Set between the input and the output are a switch ( 7 ) and a limitation block ( 9 ) which controls the switch ( 7 ) to cause at least partial inhibition thereof in the event of overcurrent. Moreover provided is a microprocessor ( 13 ) connected to the limitation block ( 9 ) to inhibit power supply to the load (Z).

[0001] The present invention relates to an electronic circuit breaker for interrupting electric power supply to a user circuit when the current exceeds a pre-set value, for instance in the case of a short circuit.

[0002] There currently exist various types of circuit breakers for protecting circuits from overcurrents. Some of these circuit breakers are of a thermal type and are based on the use of bimetallic strips, the deformation of which, on account of the dissipation of heat by the Joule effect due to the passage of current, causes opening of the circuit by a switch. In other circuit breakers, those of the electromagnetic type, interruption is caused by the movement of an armature under the effect of a magnetic field generated by a coil traversed by the current. In either case, an excessive current flowing through the strip (in the case of a thermal circuit breaker) or through the coil (in the case of a magnetic circuit breaker) causes tripping of the circuit breaker.

[0003] Thermal circuit breakers present the drawback of having a high tripping time and of being considerably unreliable owing to the effect that ambient-temperature variations can have on their operation even when appropriate measures are taken to offset the effect of these variations.

[0004] Magnetic circuit breakers can be built in such a way that they trip very fast, this being necessary for protecting present-day circuits that comprise solid-state components. However, their tripping speed is not altogether satisfactory. In addition, their reliability is low in that they feel the effects of external factors, such as variations in temperature, mechanical vibrations, magnetic interference, etc. In addition, the presence of a mobile armature sets limits to the freedom of choice of the position in which these circuit breakers can be installed, on account of the influence that the force of gravity may have on the tripping characteristics of these devices.

[0005] There also exist electronic circuit breakers, for example of the type described in U.S. Pat. No. 4,979,068. Also these circuit breakers are not altogether satisfactory.

[0006] A purpose of the present invention is to provide an electronic circuit breaker which overcomes the drawbacks presented by traditional circuit breakers.

[0007] In particular, a purpose of the present invention is to provide a reliable electronic circuit breaker that has characteristics of high durability and very short tripping times and enables limitation of peak current.

[0008] A further purpose of the present invention is to provide a device that can be programmed.

[0009] These and further purposes and advantages, which will emerge clearly to a person skilled in the art from the ensuing text, are basically obtained with an electronic circuit breaker comprising:

[0010] between the input and the output of the circuit breaker at least one switch and one limitation block which controls said switch to cause at least partial inhibition in the event of overcurrent;

[0011] a microprocessor connected to said limitation block to cut off power supply to the load connected to the circuit breaker.

[0012] In this way, an overcurrent causes tripping of the limitation block and at least partial opening of the circuit by the switch, for example a MOSFET. The tripping time is extremely short, i.e., of the order of hundreds of microseconds. Within a delay time that may be advantageously programmed by the microprocessor, the latter sends the circuit breaker into a state of inhibition and cuts off supply to the load. The circuit breaker can now be reset by means of the reset signal of the microprocessor, once the cause of its tripping has been determined.

[0013] The use of a microprocessor enables a plurality of functions and advantages to be achieved. In particular, the delay in intervention of the switch, which brings about complete inhibition or interruption of the circuit breaker (the so-called “tripping”), and the value of the current that causes opening of the circuit by the circuit breaker are programmable and may possibly be modified also remotely by means of an input/output terminal of the microprocessor and a serial port. The operating parameters of the circuit breaker (voltage at the terminals, current) can be stored and then read whenever necessary by means of the same input/output terminal and the same serial port that enable programming. The circuit breaker can be remotely controlled.

[0014] The circuit breaker according to the invention presents numerous advantages as compared to circuit breakers of the prior art. In the first place, it is more reliable, with an MTBF up to five times higher than that of other known circuit breakers. The current is limited in extremely short time intervals, even during the tripping time, i.e., the time interval up to complete opening of the circuit. The programmability of the device renders it extremely versatile. Furthermore, as will be clarified in what follows, by using the microprocessor it is possible to provide various functions without the need for auxiliary components. In particular, it is possible to detect the input voltage of the circuit breaker and program opening of the circuit by means of the microprocessor when the voltage oversteps a given value, which is programmable. This renders superfluous the use of other electromechanical devices that are sensitive to overvoltages. The current that flows through the circuit breaker can be determined by the microprocessor itself and communicated to the outside world; this fact eliminates the need for separate current sensors.

[0015] Further advantageous features and embodiments of the invention are specified in the attached dependent claims.

[0016] A better understanding of the invention will be provided by the ensuing description and the attached drawing, which illustrates a possible, non-limiting, embodiment of the invention. In the drawings:

[0017]FIG. 1 shows a block diagram of the circuit breaker according to the invention;

[0018]FIG. 2 shows a more detailed diagram of an embodiment of the invention; and

[0019]FIG. 3 shows the current-time characteristic of the circuit breaker according to the invention.

[0020] With reference initially to the diagram in FIG. 1, the circuit breaker, designated as a whole by 1, has an input consisting of two terminals, A and B, and an output consisting of two terminals, C and D. On the line A-C there is set a block 3 which contains a current-read resistor 4, by means of which the current that traverses the circuit breaker and that supplies a load circuit, or load, which is connected between the output terminals C and D, is read. The block 3 moreover contains at least one fuse 5 and one electronic switch 7. The fuse 5 constitutes a so-called “catastrophic protection”; i.e., it blows, so interrupting definitively the passage of current, for example in the event of a short circuit. In this case, the device must be replaced, or at least the fuse must be replaced, whereas in other tripping situations, as will be clarified in what follows, it is sufficient to reset the circuit breaker that has tripped on account of an overcurrent. The electronic switch 7, for example a MOSFET, constitutes a protection against transient overcurrents, and opens the circuit in the way described in what follows.

[0021] The reference number 9 designates a limitation block which comprises an operational amplifier 11 and is connected both to the block 3 and to a microprocessor 13. The limitation block 9 and the microprocessor 13 are supplied by an auxiliary voltage generator 15.

[0022] In addition to being connected to the limitation block 9, the microprocessor 13 is also connected to the block 3 and to a resistor 17 that can vary with temperature, for example a PTC or an NTC resistor, which is thermally coupled to the components of the circuit breaker that are subject to overheating.

[0023] Operation of the device outlined above is as described in what follows. In conditions of normal supply to the load Z (applied to the terminals C, D of the device), a current I_(N) is supplied. The fuse 5 is intact, and the MOSFET 7 is in full conduction.

[0024] In the case of a catastrophic event, such as a short circuit, the fuse 5 causes the circuit breaker 1 to open the circuit instantaneously and irreversibly, and power supply to the load is thus interrupted.

[0025] In the event of overcurrent to the load Z, i.e., in the event of the current exceeding a pre-set limit value I_(limit), the limitation block 9, by means of the operational amplifier 11, sends the MOSFET 7 of the block 3 into a condition of partial inhibition. The time required for this inhibition to occur is very short, i.e., in the region of 300 microseconds or even less. The current that is now flowing through the circuit breaker is kept below a value I_(limit) for a delay time that can be programmed by means of the microprocessor 13. Once this time interval has elapsed, the microprocessor 13 causes complete inhibition of the MOSFET 7 or other equivalent switching device, so bringing the current on the load to a stand-by value I_(stand-by) that is very limited.

[0026]FIG. 3 shows the tripping characteristic of the circuit breaker in these conditions. The time appears on the abscissa, and the current values appear on the ordinate, as indicated above. The graph shows the plots of the nominal or rated current I_(nom) and the maximum current I_(max) for which the circuit breaker is designed. The peak-current value is designated by I_(peak), this value being reached in a very short time interval Ts, i.e., the time needed for the limitation block 9 to go into action. The delay time between intervention of the limitation block 9 and intervention of the microprocessor 13 (tripping) is designated by Td.

[0027] The resistor 17, which is variable according to the temperature, constitutes a temperature sensor for the microprocessor 13, said temperature sensor enabling interruption of power supply in the event of overheating, by means of appropriate programming of the microprocessor itself.

[0028] Since the microprocessor 13 is connected to the block 3, it can determine, by means of the current-read resistor 4, the current instantaneously flowing through the circuit breaker. A connection between the terminals A and B moreover enables the instantaneous voltage to be read, and hence enables opening of the circuit, which is controlled by the microprocessor itself, also in the event of overvoltage.

[0029]FIG. 2 presents a more detailed diagram of an embodiment of the circuit breaker according to the invention, in which there are shown only the components that are essential for enabling understanding and reproduction of the invention. The same reference numbers designate parts that are the same as or correspond to those appearing in the block diagram of FIG. 1.

[0030] The circuit of FIG. 2 comprises three blocks, indicated by 3A, 3B, 3C, that are functionally equivalent to block 3 of FIG. 1, the said blocks being connected in parallel together and being basically the same as one another. The blocks 3 may vary in number according to the maximum current for which the circuit breaker has been sized. The larger the current for which the circuit breaker is to be sized, the greater the number of blocks 3, 3A, 3B, 3C, . . . , set in parallel, each being traversed by a fraction of the total current supplied to the load Z.

[0031] Each block 3A, 3B, 3C comprises an operational amplifier 11, the output of which is connected to the gate terminal of the MOSFET 7. The source terminal of the MOSFET 7 is connected to the terminal A of the circuit breaker 1, whilst the drain terminal is connected to the terminal C. The current-read resistor is designated by 4, and the fuse is designated by 5, both of these being set between the source terminal of the MOSFET 7 and the terminal A of the circuit breaker 1. Set between the output of the operational amplifier 11 and the gate terminal of the MOSFET 7 is a further protection fuse 21, which is set in series to a parallel-RC cell.

[0032] The inverting input of the operational amplifier 11 of each block 3A, 3B, 3C is connected, by means of a resistor 22, between the current-read resistor 4 and the fuse 5, whilst applied to the non-inverting terminal of the amplifier itself is a reference voltage V_(ref), which is generated by a circuit, designated as a whole by 23, which is connected to the microprocessor 13 and is described in greater detail in what follows.

[0033] The voltage across the current-read resistor 4 is applied to the inputs of an operational amplifier 25, the output of which is connected to the microprocessor 13, which thus receives a signal that is proportional to the current flowing through the resistor 4. The circuit arrangement described so far is envisaged only for the block 3A, whereas it is absent in the blocks 3B and 3C. Since the three blocks 3A, 3B, 3C are basically the same, the total current supplied to the load Z is equal to three times the current read by the microprocessor 13 by means of the current-read resistor 4 through the amplifier 25.

[0034] In the circuit diagram of FIG. 2, two terminals 27 are shown, which are connected, by means of an interface 28, to an input/output terminal 29, which constitutes a connection of the microprocessor 13 with the outside world. By means of this interface, the microprocessor 13 can be programmed and interrogated, for example to check the operating conditions of the device. Interrogation and programming can be carried out also remotely.

[0035] The reference number 31 designates a reset terminal of the microprocessor 13, whilst 33 designates a terminal via which the microprocessor 13 is connected to the blocks 3A, 3B, 3C. More in particular, the terminal 33 is connected to the inverting input of each operational amplifier 11 of the various blocks 3A, 3B, 3C through a transistor 35 and a corresponding diode 37. Connection between each diode 37 and the corresponding inverting input of the corresponding operational amplifier 11 is represented by the letter X.

[0036] Also shown in the diagram of FIG. 2 are two LEDs, 41 and 43, which are connected to corresponding pins of the microprocessor 13 and which enable display of the operating conditions of the circuit breaker 1, and a storage block 45 connected to the microprocessor 13, in which the information regarding the operating conditions of the circuit breaker 1 is stored, this information being readable by means of the input/output terminal 29.

[0037] The circuit 23 comprises an operational amplifier 24, the inverting input of which is connected to the microprocessor 13, and on the output of which there is present the reference voltage V_(ref). The value of the latter is programmable by means of the microprocessor 13 according to the characteristics that the circuit breaker 1 is to possess.

[0038]FIG. 2 is a schematic representation of the configuration, in itself known, of the auxiliary voltage generator 15, connected to the two terminals A and B of the circuit breaker 1. The auxiliary voltage generator 15 generates two DC voltages, e.g., 12 V and 3 V, on the terminals designated by V_(cc) and 3V. These voltages are used to supply the various circuit components, according to what is illustrated in the diagram of FIG. 2.

[0039] In line with what has been briefly described with reference to the block diagram of FIG. 1, the circuit of FIG. 2 operates as described in what follows. In normal operating conditions, the current flows through the blocks 3A, 3B, 3C towards the load Z. The MOSFETs 7 are in full conduction. In the event of overcurrent, there is the intervention of each of the operational amplifiers 11. The value at which the latter go into action is fixed by the reference voltage V_(ref), which is determined by a corresponding programming of the microprocessor 13. The time for intervention of the individual operational amplifiers 11 is very limited (less than 300 microseconds), and they have the effect of reducing the current flowing from the terminal A to the terminal C towards the load. After a programmable delay time, the microprocessor 13 goes into action, by means of the output voltage on the pin 33 sent to the individual amplifiers 11 of the blocks 3A, 3B, 3C, and sends the individual MOSFETs 7 into a state of inhibition, thus reducing the current to the tripping value I_(stand-by). The microprocessor can act on the blocks 3, causing inhibition of the switches 7 also in the case of overheating, which is detected by the resistor 17, which is temperature-variable.

[0040] It is understood that the drawings only illustrate a possible exemplification of the invention, which may vary in its embodiments and arrangements without thereby departing from the scope of the underlying idea. The possible presence of reference numbers in the attached claims has the purpose of facilitating reading thereof in the light of the foregoing description and of the attached drawings, and in no way limits the scope of protection represented by the claims. 

1. An electronic circuit breaker with an input (A, B) for connection to a power-supply network and an output (C, D) for connection to a load (Z), comprising: between said input and said output at least one switch (7) and a limitation block (9) which controls said switch (7) to cause at least partial inhibition thereof in the event of overcurrent; and a microprocessor (13) connected to said limitation block (9) to cut off power supply to the load (Z).
 2. The circuit breaker according to claim 1, wherein said limitation block (9) comprises an operational amplifier (11), to a first input of which there is applied a signal proportional to the current that traverses said circuit breaker, and to the second input of which there is applied a reference voltage (V_(ref)).
 3. The circuit breaker according to claim 2, wherein said reference voltage is programmable by means of said microprocessor (13).
 4. The circuit breaker according to claim 2 or 3, wherein said microprocessor is connected to the inverting input of said operational amplifier (11).
 5. The circuit breaker according to claim 2, or 3 or 4, wherein said switch (7) is connected to the output of said operational amplifier.
 6. The circuit breaker according claim 5, wherein a fuse is set between the output of said operational amplifier and said switch.
 7. The circuit breaker according to one or more of the foregoing claims, comprising at least one catastrophic-protection device (5) between its input and its output.
 8. The circuit breaker according to one or more of the foregoing claims, comprising at least one read resistor for determining the amount of current that flows through said circuit breaker.
 9. The circuit breaker according to claim 7, wherein said at least one catastrophic-protection device (5) is set in series to said at least one switch.
 10. The circuit breaker according to claim 8, wherein said at least one read resistor is set in series to that at least one switch.
 11. The circuit breaker according to one or more of the foregoing claims, wherein said microprocessor is programmable for intervening with a pre-set delay with respect to the partial inhibition of said switch.
 12. The circuit breaker according to one or more of the foregoing claims, wherein said microprocessor is connected to a temperature sensor and is programmed to cause opening of the circuit in the event of overheating.
 13. The circuit breaker according to one or more of the foregoing claims, wherein said microprocessor (13) comprises an input/output terminal (29) for programming and/or communication with the outside world.
 14. The circuit breaker according to one or more of the foregoing claims, wherein said microprocessor is associated to a memory for storing the parameters for operation of the circuit breaker.
 15. The circuit breaker according to one or more of the foregoing claims, comprising a plurality of switches (7), each of which is associated to a corresponding limitation block (9), said switches (7) being set in parallel with respect to one another.
 16. The circuit breaker according to one or more of the foregoing claims, wherein said microprocessor receives at input a signal proportional to the voltage at input to the circuit breaker and is programmed in such a way as to cause opening of the circuit by the circuit breaker when said voltage exceeds a pre-determined value. 